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JTAGProgrammer - SVF Generation: what do the two options for the initial transition to Run-Test/Idle mean?

Description

General Description:When selecting to create an SVF via the JTAG Programmer, there are two options for the initial transition to Run-Test/Idle. These options are:

a) through Test-Logic-Reset b) skipping Test-Logic-Reset

What do each of these options mean, and how does it affect the SVFgeneration?

Solution

JTAG Programmer generates an initial "STATE" command in the SVF. The SVF "STATE" command tells a JTAG controller to take the TAP state machine to a particular state.

Option (a) generates: STATE RESET IDLE;

Option (b) generates: STATE IDLE;

For option (a), the RESET in the "STATE" command suggests to the JTAGcontroller that it should select a path through the TAP state machine that passes through the Test-Logic-Reset state on its way to the Run-Test-Idle state.

Only when the user can, and wants to control the TAP state sequencing for special purposes should you select the "skipping Test-Logic-Reset" option.

Typically, the option selection does not matter. Test-Logic-Reset incurs no unusual effects in Xilinx devices. In most cases, the JTAG controllers force the TAP controller through Test-Logic-Reset on startup to insure a known starting state. Furthermore, most JTAG controllers ignore the intermediatestate paths within an SVF "STATE" command and proceed to the final state on their own terms. In fact, the initial transition option has no affect among the supported ATE nor XSVF (Xilinx XAPP058) solutions.